Factor negative 7 x cubed plus 21 x squared plus 3 x minus 9 by grouping. What is the resulting expression?

Group the terms in pairs: (−7x³ + 21x²) + (3x − 9). Factoring each pair gives −7x²(x − 3) + 3(x − 3), so the common factor is (x − 3). The result is (3 − 7x²)(x − 3), which is choice C.

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